1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display capable of reducing a distortion of a common voltage.
2. Discussion of the Related Art
An active matrix type liquid crystal display displays a motion picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal display has been implemented in televisions as well as display devices in portable devices such as office equipments and computers, because of the thin profile of the active matrix type liquid crystal displays. Accordingly, a cathode ray tube (CRT) is being rapidly replaced by the active matrix type liquid crystal display.
In the active matrix type liquid crystal display, a data voltage is applied to pixel electrodes, and a common voltage is applied to common electrodes opposite the pixel electrodes. The common electrodes are connected in parallel to common lines. Liquid crystal cells are driven by the voltages applied to the pixel electrodes and the common electrodes.
However, the common voltage is easily distorted by a deviation between resistances of the common lines or a deviation between the common voltages over the entire surface of a liquid crystal display panel based on a structure of the common lines. For example, in a liquid crystal display in which as many common lines as the number of horizontal lines (i.e., a vertical resolution) are formed parallel to gate lines, because a data voltage is simultaneously applied to pixels of 1 horizontal line through the supply of scan pulses, a load of the common lines opposite the pixels increases. Because the load of the common lines depends on an amount of RC delay defined by a multiplication of a resistance and a parasitic capacitance of the common line, the resistances of the common lines have to be reduced so as to reduce the amount of RC delay. However, as shown in FIG. 1, because a related art liquid crystal display is configured to receive a common voltage Vcom through only two input sources, it is limited to a reduction in resistances of common lines. As a result, as shown in FIG. 2A, the common voltage Vcom is not kept constant and is affected by a scan pulse SP or a data voltage Vdata. Hence, a ripple phenomenon is generated in the common voltage Vcom. The ripple phenomenon of the common voltage Vcom is a main cause generating a horizontal crosstalk when a specific data pattern is displayed on the screen as shown in FIG. 3A.
In the related art liquid crystal display, as the common lines go from right and left sides of the liquid crystal display panel to a middle portion of the liquid crystal display panel, the resistances of the common lines increase because of the structure of the common lines shown in FIG. 1. Therefore, as shown in FIG. 2B, a deviation of the common voltage Vcom over the entire surface of the liquid crystal display panel is caused. As shown in FIG. 3B, the deviation of the common voltage Vcom causes a difference between luminances of upper and lower portions of the liquid crystal display panel and a flicker, and also accumulates DC components inside the panel to thereby generate image sticking. In most of liquid crystal displays, common lines formed at edges (i.e., a non-display area outside a pixel array) of a liquid crystal display panel are configured to have a wide width so as to reduce the resistances of the common lines. However, it is limited to a reduction in the resistances of the common lines because of a limitation in the size of the non-display area. Further, there is a relatively large deviation between resistances of the common lines depending on a location of the common lines.
Further, because the related art liquid crystal display uses a DC level common voltage, a voltage corresponding to one half of a high potential power voltage input to a data driver integrated circuit (IC) may be used as a liquid crystal driving voltage in an inversion scheme. In other words, the data driver IC requires an output voltage equal to or greater than two times the liquid crystal driving voltage. Hence, it is difficult to secure a driving voltage margin of the data driver IC and to reduce a power consumed in the data driver IC.